This invention relates to recording mediums displaying a high resolution multicolor pattern. These recording mediums are especially used in the formation of microtopographical maps.
The recording of multicolor images is described in U.S. Pat. No. 3,727,233. The recording medium disclosed in this patent is made by applying a metal layer of high reflectivity to a glass substrate and covering this metal layer with an organic polymer layer. The desired pattern is formed on the polymer layer by exposing it to electron beams. The irradiation intensity of the electron beams determines the pattern formed by the polymerization of the layer. Over the polymer layer, another metal layer of high reflectivity is applied. The interference patterns yield a multicolor image when viewed under natural light. One disadvantage of this method is that the metal layers are of equal thickness over the entire substrate, thereby permitting no variations in the saturation of the individual colors of the image. The patterned interference layer formed by the organic polymer is very heat sensitive. Because of this and the high elimination strength associated with this, strong reenlargement (Ruckvergrosserung) of the multicolor image is not permitted. The deficient lightfastness and shrinkage of the organic polymer interference layer over time can cause the colors to change.
The German unexamined patent specification No. OS 26 58 623 discloses a recording medium which records with high information density. This recording medium is particularly used for multicolor micro-images. At least two interference filters (Interferenzfilter) for two different colors are applied onto the substrate of this recording medium. Each of the interference filters is made with an unpatterned inorganic absorption-free interference layer which extends with equal thickness over the entire substrate. This inorganic interference layer is bounded on each side by at least one inorganic reflecting layer which forms the pattern of the recording. In another embodiment disclosed in this patent specification, the unpatterned interference layer is bounded on each surface by at least one patterned, high-refracting absorption-free layer. Between every two high-refracting layers there is present an unpatterned, low-refracting absorption-free layer. The presence of the unpatterned interference layers which extend with equal thickness over the entire substrate in the different embodiments of this patent specification, incurs the requirement that for each desired color a series of patterning steps is necessary. During this process the exposure mask must be adjusted for each patterning step, requiring the greatest of precision. The adjustment of the exposure mask is also very time consuming.